1. The Field of the Invention
The invention is in the field of compositions and methods for sealing a root canal during an endodontic procedure. More particularly, the invention involves compositions having enhanced adhesion to hydrophilic dental tissues found within root canals which assists their ability to effectively seal and protect a newly cleaned root canal. Such compositions are preferably radiopaque and are cured more rapidly compared to existing endodontic sealing compositions, thus allowing for quicker placement of a final filling or crown to complete the root canal procedure.
2. The Relevant Technology
Following an endodontic root canal procedure, in which the root canal is cleaned using special root canal tools and irrigation devices, it is important to fill and seal the evacuated root canal in order to preserve the dead tooth from further decay that might compromise the integrity of the tooth and cause infection. In a typical procedure, one or more soft, resilient, needle-like inserts known as xe2x80x9cgutta perchaxe2x80x9d points are inserted in each root canal branch in order at least partially seal and fill the root canal.
The term xe2x80x9cgutta perchaxe2x80x9d refers to a rubbery material derived from natural rubber, typically blended with zinc oxide. This particular rubbery material is preferred because it is compressible, flexible and relatively soft so that it can be used to fill voids within the exposed root canal. The gutta percha points are typically impregnated with other materials such as radiopaque solids, zinc oxide, for its medicinal properties, and other passive or active ingredients as desired. It is impossible, however, to completely seal a root canal from all ingress of fluids, which may be laden with bacteria, using gutta percha alone. Conventional techniques require multiple gutta percha cones per canal and laborious xe2x80x9clater condensationxe2x80x9d techniques. For some, it requires a heating the gutta percha in an attempt to make it flow into the lateral canals. However, this technique, coupled with the properties of gutta percha, make it hard to achieve fine adaptation to canal walls and flow into the dentinal tubules.
The filling and sealing of the root canal can be further enhanced by inserting flowable materials, such as antiseptic pastes and/or sealing resins along with the gutta percha points. Due to the high viscosity of typical antiseptic pastes, such as zinc oxide/eugenol, or sealing resins, which tend to be epoxy-based, such materials are first applied to the gutta percha and then inserted into the root canal along with each gutta percha point. Alternatively, they may be inserted using a lentalo applicator. In this manner, it is hoped that the remaining spaces between the gutta percha points and the root canal can be filled with the antiseptic paste or resin. In addition, it is hoped that the epoxy-based resin will help to seal the root canal.
One of the drawbacks of using conventional pastes or resins is that such materials tend to be hydrophobic. This renders such materials somewhat incompatible with dental tissues within the root canal, which are highly mineralized, somewhat moist and therefore extremely hydrophilic. The hydrophilic nature of the root canal environment inhibits wetting and adhesion of the root canal by hydrophobic materials. As a result, conventional antiseptic pastes and epoxy-based resins actually form a poor seal between the gutta percha points and the walls of the root canal, thus potentially providing access for microbes and infection.
A further problem of conventional antiseptic pastes and epoxy-based endodontic sealing resins are their inability to adequately penetrate into, wet and seal the lateral canals which extend laterally from the root canal into the root of the tooth. Occasionally, the inability to seal the lateral fissures using conventional pastes and/or epoxy-based resins creates one more place where microbes may establish a beach head and be capable of festering over time.
In addition to the inability of the antiseptic pastes or epoxy-based resins to adequately adhere to and seal the root canals and lateral fissures, another problem relates to the inability to evacuate all air bubbles or pockets from the root canal during placement of the gutta percha points and associated pastes or resins. As the gutta percha point coated with pastes or resins is packed into the root canal, or as sealers are worked in with a lentalo applicator, upper portions of the gutta percha or sealer can seal against the root canal wall, thus trapping air between the coronal portion and the root canal apex. Failure to remove such air pockets creates an area where subsequent infection can fester. Although gutta percha is highly radiopaque, even if the dentist can observe whether or not the root canal spaces have been adequately filled, the task of removing the packed materials and repeating the procedure is time consuming, expensive, and uncomfortable for the patient. Moreover, many sealer pastes are only moderately radiopaque and include silver powder, which makes the root canal too dark.
Lateral condensation using gutta percha is typically not sufficient to force the highly viscous pastes, gutta percha, or resins into the lateral canals. Merely pushing against the top portion of the gutta percha does not exert very much force on the flowable pastes or resins, since pressurized fluids can escape around the space between the gutta percha, lateral condensation instrument, and the root canal rather than being forced into the lateral canals or other areas occupied by air bubbles or pockets.
Finally, in the case where nonpolymerizable pastes, such as zinc oxide/eugenol are used, the chemistries of such materials can interfere with the ability of subsequently placed prosthetic filling materials to chemically bond or adhere to the tooth.
In short, it would be an improvement of the art of endodontic procedures to provide compositions and methods which improved the ability of an endodontic sealing material to penetrate, wet, adhere and seal to the dental tissues surrounding or defining the root canals.
It would be an additional improvement in the art to provide compositions and methods that provided for a more thorough evacuation of air bubbles or air pockets within the root canal, as well as including lateral spaces or canals connected to or in communication with the main root canal branches.
It would also be an improvement in the art to provide compositions and methods which yielded a filled root canal in which the sealing material did not interfere with the ability of a subsequently placed composite resin material to bond or adhere to the tooth.
It would be a further advancement in the art if such compositions and methods provided for the ability to allow for variable curing times such as faster or slower curing, to account for variations in difficulty and success that may be experienced by a dental practitioner.
It would yet be an improvement in the art if such compositions could also be light cured so as to reduce the time a patient must wait until the root canal sealing material was sufficiently cured to permit subsequent filling of the remainder of the tooth with a composite filling material.
Such compositions and methods for more effectively filling and sealing a root canal and providing a bonding surface are disclosed and claimed herein.
The present invention encompasses adhesive resins for use in filling and/or sealing a root canal during an endodontic procedure, as well as procedures that employ such compositions. The adhesive sealing and filling resins according to the present invention include a component that is compatible with a hydrophilic environment and that allows the resin to wet, penetrate and adhere to the dental tissue surrounding the root-canal. In addition, such resins are better able to penetrate into and seal the lateral canals that often extend from the main root canal branches. In order to assist such sealing, improved methods for applying a pressure to the sealing and filling resins are also disclosed.
The adhesive sealing and filling compositions of the present invention include one or more polymerizable methacrylate monomers, preferably including an oxyphosphorus constituent for better adhesion, a radio opacifying agent, and one or more types of polymerization initiators. The composition may also include other additives such as diluent or complementary monomers, fillers, antimicrobial agents, plasticizers, solvents and the like.
An example of an adhesive methacrylate resin within the scope of the invention is bis-glycidyl dimethacrylate phosphate. An example of a radio opacifying agent according to the present invention is bismuth chloride. An example of a suitable diluent monomer is urethane dimethacrylate. Examples of polymerization initiators include chemical initiators, such as peroxides and amines, and photoinitiators, such as camphor quinone. Because it is typically impossible to completely cure a polymerizable resin using photo initiation as the sole means to initiate polymerization, particularly all the way down to the apex of the root canal, it will typically be advantageous to include a chemical initiator so as to ensure complete curing of the polymerizable monomer over time.
In a preferred embodiment, the chemical initiator will be selected and included in an amount so as to provide sufficient time for a dental practitioner to properly place the composition within the root canal and ensure good penetration into the lateral canals. In most cases, it will be advantageous to include a chemical curing agent that causes the polymerizable resin to cure within a time period of from about 15 minutes to about 2 hours, more preferably from about 30 minutes to about one hour.
In the event that the dentist determines that the endodontic sealing resin has been properly placed, the dentist can then rapidly cure the upper portion of the resin by means of the inclusion of a photoinitiator and the application of curing radiation, such as light generated by a conventional dental curing lamp. In this way, the dentist can cure the top few millimeters of endodontic sealing resin by means of the curing lamp so as to provide a hardened upper surface to which a composite filling material can be chemically bonded or adhered. This greatly speeds up the time in which a dentist can complete the endodontic procedure.
In the case of resins or sealers that are only chemically cured, the dentist must ensure adequate curing and solidification prior to placing a composite resin on top of the sealing resin. In some cases, the patient must sit in the dental chair for half an hour, to an hour or more, wasting both the dentist""s and the patient""s time. In many cases, the dentist will simply place a temporary filling material over the uncured resin and send the patient home with the result being the patient must return for a follow-up visit in which the dentist removes the temporary filling material and replaces it with the final restorative material.
Embodiments that include xe2x80x9cdual curexe2x80x9d compositions (i.e., compositions that are capable of both chemical and light cure) provide a tremendous advantage over single cure resins. Although such dual cure capability has been available for luting cements, it has never been available for root canal sealing or filling materials. The chemical cure properties provide the aforementioned window of time to account for variations in procedure difficulty and success, while the light cure properties provide for almost immediate curing of the top layer by photoinitiated curing once it has been determined that the sealing or filling material has been properly placed. This provides a tremendous advantage for both the dentist and the patient because it obviates the need for a patient to either sit in the dental chair wasting time while the resin cures or else having to make a return visit to receive the final filling material. Another advantage is that the resins chemically cure in a relatively short period of time compared to conventional sealers, thus minimizing the tendency of monomers to leach into the surrounding tissue.
In another aspect of the invention, the adhesive resins are placed within the root canal by means of a narrow cannula or syringe tip device attached to a high pressure hydraulic device or system. Due to the viscosity of the mixed polymerizable resins or non resinous pastes such as zinc oxide pastes, coupled with the small size of typical root canals, it is difficult to express sealing resins or pastes through cannulas or syringe tips capable of entering into a root canal. For this reason, the inventive methods according to the present invention contemplate the use of high pressure syringes or other hydraulic devices, such as those disclosed in copending U.S. application Ser. No. 09/467,419, filed Dec. 20, 1999, and presently assigned to Ultradent Products, Inc. For purposes of disclosure, the foregoing U.S. patent application is incorporated herein by specific reference.
In a preferred method for placing adhesive resins within a root canal, the apex of the root canal is first sealed using a gutta percha cone. In order to ensure that the apex has been adequately sealed, a xe2x80x9ctug backxe2x80x9d seal is formed. That is, the gutta percha cone is first inserted and then removed. If it can be removed with little or no force, the gutta percha point is trimmed to yield a larger diameter tip and reinserted into the apex. This process is repeated until there is xe2x80x9ctug back,xe2x80x9d thus indicating that the fit between the gutta percha point and the apex is sufficiently tight to adequately seal the apex and prevent flow of sealing or filling material therethrough into the surrounding bone tissue.
After sealing the apex, the sealing or filling resin is inserted into the root canal using a narrow cannula tip. The cannula tip is placed within the root canal near the apex and slowly raised as the root canal is filled with resin, thus minimizing or eliminating the formation of air pockets or bubbles as the sealing or filling resin is progressively placed within the root canal. This procedure greatly improves the ability of the resin to initially purge most or all of the air from within the root canal compared to simply dipping a gutta percha point in the resin and stuffing the point into the root canal, or spinning the material with lentalo applicators, as is typically done using conventional methods.
In order to further ensure that the endodontic sealing resin penetrates and seals every space, irregularity, or lateral canal of the root canal, it may be advantageous to apply pressure to the resin after it has been initially placed within the root canal. This may be accomplished, for example, by inserting a plunger of complimentary size into the hole previously bored through the crown of the tooth. The plunger will typically include a plunger rod and a resilient plunger plug, such as a plug made of gutta percha material. In a preferred method for forming a plunger, excess gutta percha material trimmed from a gutta percha cone used to fill a root canal is wrapped around the end of a stiff metallic wire or plunger rod. The wire and gutta percha are then placed through the hole of the tooth. The wire is heated, which momentarily causes the gutta percha to melt and coalesce together, thus forming a resilient plunger plug having a size complementary to the hole in the tooth.
Inward pressure of the plunger from the crown toward the apex of the root canal exerts pressure on the resinous sealing material, thus forcing the material into the cracks, crevices and lateral canals of the root canal. Because the resilient gutta percha plug seals against the walls defining the hole through the crown of the tooth, the resinous material is not able to squeeze out between the tooth and the gutta percha plug but is instead forced into the aforementioned spaces, crevices or canals. In this manner, the resinous sealing or filling material is able to substantially form a hermetic seal of the root canal.
Providing a more complete seal of the root canal greatly increases the ability of the sealed root canal to resist the ingress of fluids into the root canal. Such fluids, if allowed to enter a root canal, may introduce microbes capable of infecting the tooth and surrounding bone. In improving the ability of the resinous sealing material to actually seal the root canal, including lateral canals and other crevices typically hard to fill, the inventive compositions and methods provide a tremendous advantage over conventional compositions and methods in yielding a tooth that is more resistant to microbial leakage.
In view of the foregoing, it is an object of the invention to provide compositions and methods which improve the ability of an endodontic sealing material to wet, adhere and seal to the dental tissue surrounding or defining the root canals.
It is an additional object of the invention to provide compositions and methods that provide for a more thorough evacuation of air bubbles or air pockets within the root canal, as well as lateral spaces or canals connected to, or in communication with, the main root canal branches.
It is also an object of the invention to provide compositions and methods which yield a filled root canal having a material to which a subsequent composite resin material can chemically bond or adhere.
It is a further object of the invention to provide compositions and methods which provide for variable curing times, such as faster or slower curing, to account for variations in difficulty and success that may be experienced by a dental practitioner.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.